A liquid crystal display (LCD) has advantages of thin shape, light weight and low consumption of electric power, compared with a cathode ray tube (CRT). Most of the commercially available liquid crystal displays usually use a twisted nematic liquid crystal. A liquid crystal display mode is classified into a birefringent mode and an optical rotatory mode.
In a liquid crystal display of a birefringent mode, alignment of liquid crystal molecules is twisted over 90.degree.. The transmittance of the super twisted nematic (STN) liquid crystal display is changed abruptly over a threshold voltage when applying voltage to the cell. Accordingly, the liquid crystal display of the birefringent mode can display a large image by a time-sharing addressing method, even though an electrode consists of a simple matrix without an active matrix (such as a thin layer transistor or diode). However, the liquid crystal display using the super twisted liquid crystal molecule has a slow response speed (several hundreds milliseconds). Further, it is difficult for the simple matrix to display a gray scale image.
A liquid crystal display having an active matrix (e.g., TFT-LCD, MIM-LCD) uses a liquid crystal molecule twisted at 90.degree. of an optical rotatory mode. The twisted nematic liquid crystal display (TN-LCD) has a fast response speed (several ten milliseconds). Further, the TN-LCD can display an image of high contrast. Therefore, the TN-LCD is predominant over commercially available liquid crystal displays.
Color and contrast in an image displayed in a conventional liquid crystal display depend on the viewing angle. A liquid crystal display is inferior to CRT in the viewing angle dependence.
An optical compensatory sheet is used to remove color formed in a liquid crystal cell. An optical compensatory sheet of a specific optical characteristic has another function of enlarging a viewing angle of a liquid crystal display.
A stretched birefringent film has been used as the optical compensatory sheet. Japanese Patent Provisional Publication No. 6(1994)-75116 and European Patent No. 576, 304A1 disclose an optically negative uniaxial compensatory sheet (a stretched birefringent film) having an inclined optic axis. The optical compensatory sheet has the function of enlarging a viewing angle.
It has been proposed to use an optical compensatory sheet comprising a transparent substrate and an optically anisotropic layer in place of the stretched birefringent film. The optically anisotropic layer is usually formed by aligning discotic compounds and fixing the aligned compounds. The discotic compounds usually have a large bire-fringence. The discotic compounds have various alignment forms. Therefore, an optical compensatory sheet using the discotic compounds can have a specific optical characteristic that cannot be obtained by the conventional stretched birefringent film. Japanese Patent Provisional Publication No. 6(1994)-214116, and U.S. Pat. Nos. 5,583,679, 5,646,703 disclose the optical compensatory sheet using the discotic compounds.
The viewing angle of the liquid crystal display can be improved by using the above-mentioned optical compensatory sheet. However, the improved viewing angle is still inferior to that of CRT.